This invention relates to phosphors and more particularly to electroluminescent phosphors. Still more particularly, it relates to a process for improving the half-life of such phosphors.
Phosphors are a known class of materials that emit electromagnetic radiation in response to stimulation by a form of energy. Generally, the emission of the phosphors is in the visible region of the spectrum. These phosphors are delineated by the form of energy to which they are susceptible, thus: cathode ray tube phosphors are stimulated to emission by impingement of electrons; photoluminescent phosphors are stimulated to emission by actinic radiation; x-ray phosphors are stimulated to emission by the impingement of x-rays; and electroluminescent (hereinafter, EL) phosphors are stimulated to emission by placement in an alternating electric field. It is the latter type of material to which this invention is directed, particularly such phosphors based on ZaS and activated with Cu and Cl.
EL phosphors have many commercial uses such as for LCD back-light, copy machines, automotive dashboard displays, nightlights, control switch illumination, emergency lighting, watch dials, etc. Their value lies in their long life and high electrical resistance, making them very economical to operate; however, these materials, as do most phosphors, do lose some of their light output over time.
It would, therefore, be an advance in the art if the lifetimes of these materials could be increased.
It is an object of this invention to obviate the disadvantages of the prior art.
It is another object of the invention to enhance EL phosphors.
These objects are accomplished, in one aspect of the invention, by a process for improving the half-life of ZnS:Cu,Cl electroluminescent phosphor wherein the improvement comprises firing a previously first fired material comprised of ZnS:Cu,Cl with a quantity of MgSO4.7H2O to form a second fired material said quantity being from 0.015 to 0.15 mole of MgSO4.7H2O mole of ZnS.
Improvements in the half-life of phosphors so processed can be up to 14%.